Fix hidden/broken pages

[engn33r]

There are hidden/broken pages that need to be moved or deleted.

https://docs.yearn.fi/getting-started/products/yvaults/vault-tokens
https://docs.yearn.fi/getting-started/products/ybal/overview

https://docs.yearn.fi/developers/addresses/yprisma-contracts
https://docs.yearn.fi/developers/data-services/yearn-api
https://docs.yearn.fi/developers/security/risks/risk-score-legacy
https://docs.yearn.fi/developers/v2/CONTRACTS_REVIEW
https://docs.yearn.fi/developers/v2/hacking-with-yearn

https://docs.yearn.fi/contributing/governance/governance-and-operations
https://docs.yearn.fi/contributing/governance/proposal-repository
https://docs.yearn.fi/contributing/governance/veyfi
https://docs.yearn.fi/contributing/operations/decision-making
https://docs.yearn.fi/contributing/operations/osc-levels